HYPURGON SKEATI. 781 



neural gland lias a simple opening with a swollen lower lip 

 (fig. 4, d. t.). 



Through the narrow aperture of comnnmication between 

 the two regions of the body the oesophagus descends to open 

 into the stomach, while the intestine passes upwards into the 

 rectum, which lies above the constriction, so that the anal 

 opening is close to the base of the branchial chamber. 



The walls of the stomach are raised up round the termina- 

 tion of the oesophagus ; or, in other words, the oesophagus 

 has its opening deep in the cavity of the stomach ; the ter- 

 minal part of the oesophagus is richly ciliated. The intestine 

 of a young bud is frequently found attached at both ends to 

 the oesophagus, to which it owes its origin. When this is 

 the case the tlioracic portion of the same bud is to be seen 

 lying in the test at the opposite side of the oesophagus. The 

 budding is thus of the type known as pyloric (Giard), 

 and found among Didemnid^ in the tribe Didemninse (Y. 

 Delage) . 



The walls of the stomach are smooth ; seen en face from 

 the outside they show a beautiful reticulum formed of the 

 more deeply staining protoplasm which surrounds and con- 

 nects the nuclei of the cells of the gastric epithelium. 



The intestine as it leaves the stomach is richly ciliated ; in 

 passing thence to the anus its walls become continually 

 thinner, the walls of the rectum being almost membranous. 

 The anus has thickened lips. The alimentary canal is bathed 

 by blood-sinuses along its whole course. 



The heart in its pericardium runs more or less vertically 

 between the upper and lower walls of the abdominal 

 cavity. Its lower end abuts against and sends a large vessel 

 into a prominence of the test, the sides of which are covered 

 by a patch of specially large cells of the mantle which form 

 the glandular part of the renal organ (r. gl., figs. 5 and 7). 

 The excreta of these glandular cells appear to be picked up 

 by wandering cells — presumably corpuscles of the blood con- 

 tained in neighbouring vessels or sinuses. These colls would 

 then migrate into the test, carrying their burden with tliciii. 



